Aircraft attitude indicator



Dec. 24, l1946. F. D. BRADDON 2,412,961

AIRCRAFT ATTITUDE INDICATOR Filed Nov. 15, 1941 2 sheets-sheet 1- f h iO 2X GUS lNvENToR, FREDERICK D. BRADDON,

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F. D. BRADDON 2,412,961 AIRCRAFT ATTITUDLI INDICATOR Filed NOV. l5, 1941I 2 Sheets-Sheet 2 ,"7" INVENTOR, E 7 FREDERlCK D. BRADDQN, 2.25?- 4 l MH l S ATTORNE Patented Dec. 24, 1946 AIRCRAFT ATTITUDE INDICATORFrederick D. Braddon, Babylon, N. Y., assignor to Sperry GyroscopeCompany, Inc., Brooklyn, N. Y.,.a corporation of New York Application Novmber 13, 1941, Serial No. 418,943

This invention relates to gyroscopic artificial horizons orgyro-verticals primarily adapted for use to assist in navigatingaircraft. As at present designed, the gyroscopic artificial horizonfurnishes valuable information to the pilot during straight line flightin that it shows whether or not the aircraft is ying level. Whenturning, however, since the gyroscope remains horizontal, it Will showthe amountV ofv bank but furnishes no indication as to whether or notthe airplane is banked at the proper angle during a turn. In otherwords, it shows at all times the real vertical or horizontal and not thevirtual vertical or horizontal. It is therefore necessary for the pilotto correlate the indications of the horizon with those of otherinstruments (such as a ball bank indicator) to properly control a turn.

The purpose of the present invention is to improve the gyroscopichorizon so that it mayy be used at all times to show whether theairplane is in the proper attitude both when iiying straight andl whenturning, which condition is satisfied if the indicator may be madey toshow the virtual vertical during turns. For this purpose I propose tomodify the horizon indicator of a gyroscopic artificial horizonV by acorrection factor proportional to the centrifugal force of the turn.This is preferably done by incorporating on the face of the horizonadditional referencemarkings, or an index, which are displaced during aturn through an angle proportionalV to the centrifugal force (F). As Fin turning, is proportional to both angular and linear speedv (Fawn) Ipropose to displace such index by means of a rate-of-turn gyroscopewhich measures o which is suflicient for a predetermined air speed butmay be supplemented by an adjustment for other air speeds which is ameasure of 12.

Referring to the drawings showing one form my invention may assume.

Fig. 1 is a plan View of my improved gyroscopic horizon with the outercase shown in section.

Fig. 2 is a side elevation of theV same with the case in section.

Fig. 3 is a front. view of the same with the cover removed.

Fig. 4 is a front view of my device asy seen on the instrument panel, asit would appear during straight level flight.

Fig. 5 is a similar View of the. instrumentl as it would appear to theaviator during curved' flight with the, airplane banked at the properangle.

Fig. 6 isfa plan view, partly in section, similar to Fig. 1;, of amodiedform of the invention.

6 Claims. (Cl. 33-204) Fig. 7 is a similar view of a still furthermodification. I have illustrated the gyroscopic horizon as of usualform, comprising a rotor bearing casing I 'f in which the rotor (notshown) is mounted for spinning about a Vertical axis. Said casing isshown as pivoted on transverse axis 2 -2 within a gimbal ring 3, whichin turn is pivoted on a fore and aft axis 4-4 in brackets 5 and 5secured Within the outer enclosing casing 1. Air is usually employ-edito spin and erect the gyroscope, the outer casing 'I usually beingevacuated through asuctionpipe 8 and atmospheric air being admittedthrough apertures 9 connected withy appropriate passages through thesupports and trunnions to the rotor sinning jets (not shown) within thegyro casing. The used air is withdrawn from casing I through pendulumcontrol apertures 50 in an extension 5I from the casing by whicherection of the gyroscope is maintained.

The horizon indicator proper is shown in the form of a horizontal bar I0at the face of the instrument usually read in connection with indices 40andv 4I, the bar and indices formingV a two part horizon indicator,which bar is secured tora long lever II pivoted at l2 on the gimbal ring3, so that the bar is stabilized against rolling. Relative pitching ofthe gyroscopev and craft im"-A parts up and down motionl to the bar bymeans of a pin I3v extending fromV theI gyro case `through a slot I4 inthe girnbal ring, and thence toY a multiplying lever I5 pivoted at oneend I6 on the gimbal ring. At its other end, said lever is' providedvwith a pin I'I engaging a horizontal slot I8 in the lever IfI. Theresult is thatV the horizon bar moves in the same direction that thehorizon appears to move upon pitching of the craft, as is common in theart. The bar may also be read by reference to a representation 44 of anaircraft on the front window 45. fThel face of the instrument is alsoprovided with'a con-Vex mask I9 secured to the2 gimbal ring 3 so as tobe stabilized against rolling. Said mark is usually provided with anindex Zllat the top or bottom to show the amount of roll.

According to my invention, I place a movable index ring 2| on the faceof the instrument, which is under the control of some means responsiveto i `turn of the cra-ft so as to displace the ring through an angleproportional to the centrifugal force. Y

Since suchforceis proportional to wv, as above explained, I may turnsuch ring directly from a, rate-of-turn gyroscope modified by the airspeed of the craft. Tothis endl have shown a rate-of-y turn typegyroseope 22, the rotor casing 22'l of which is shown pivoted within thehousing 1 on horizontal trunnions 23, the spin axis 24 of the enclosedrotor lying normally fore and aft. Said gyroscope is shown ascentralized by spring 25 anchored to the casing 22'. With thisarrangement when the craft yaws or turns about its vertical axis, thegyro 22 precesses on its horizontal axis in one direction or the other,depending upon the direction of turn of the craft through an angleproportional to the rate of turn.

In order to introduce the linear velocity factor, such precessionalmovement of the gyroscope is shown as transferred to the ring 2| bymeans of a link 26 pivoted to a bracket 21 on the gyroscope and slidablyconnected at its forward end in a slot 28 in bell-crank lever 29 pivotedon casing 1 at 30. The distance of the pin 28 from the pivot 30 may beadjusted in accordance with the air speed either automatically or myhand as by means of a knob 3| and scale 32. Turning of the knob moves afork33 on the shaft-34 of said knob, said fork engaging the link 26 tolift oriower the free end thereof (see Fig. 3). The other leg of saidbell-crank lever is shown as in the form of a gear sector 35, the teethof which mesh with an annular crown gear sector 36 on the back of thering 2|, which is rotatably mounted in a groove 31 in bezel ring 38.When the craft turns, the gyroscope precesses to displace the ringthrough an angle proportional to the rate of the turn as modified by theair speed adjustment. Obviously, an approximate reading might beobtained without using this adjustment, merely by setting the device forthe cruising or average air speed of the craft. Ring 2| is shown asprovided with an index 39 which cooperates with the index 20 on the maskI9. The aforesaid indices 40 and 4| are also preferably placed on saidring so as to normally lie in line with the horizon bar but the aircraftoutline 44 is retained on the front window. Preferably, also, the ringis provided with angular markings 42 at the top thereof showing thedirection and rate of turn (for any selected air speed), said markingsbeing readable upon an .index 43 secured to the bezel.

When iiying a straight course, my improved horizon is used exactly thesame as the present artificial horizon and its appearance remainssubstantially unaltered, but my improved horizon may also be used duringturns since if the aircraft is banked correctly during the turn, thehorizon bar will still be lined up with the reference markings 40, 4|,and also the bank angle indication 20 will remain lined up with thereference mark 39, and the ball bank indicator will remain centralized.On the other hand, the fact that the craft is banked will still be shownby the fact that the horizon bar is no longer parallel to the image ofthe aircraft 44. My improved indicator will also show the rate of turnfor any selected airspeed by indications 42 and 43. In fact, thisindicator really moves through an angle proportional to the centrifugalforces acting on the craft (Fawn) so that it furnishes the aviator witha valuable check if dangerous acceleration forces are approached,therebyv warning him to either reduce his air speed, or increase hisradius of turn or both. The real attitude of the craft about its rollaxis is observed by comparing the relative positions of the xedrepresentation 44 and the stabilized bar I0. The virtual attitude isobserved by comparing the relative positions of the bar with the movableindices 40 and 4|'.

A somewhat simpler form of the invention is shown in Fig. 6. In thisfigure, the rate-of-turn gyroscope 22" is mounted with its trunnion axis23' fore and aft and with its spin axis 24' athwartships. In this case,the rotatably adjustable ring 2 is directly connected to the rate gyrocasing by means of a long arm B0 connected to the top of said casing. Inthis instance, however, the air speed adjustment is made by varying thetension of the centralizing spring 25Vconnected to the gyroscope, thetension being increased inversely with air speed. For this purpose theouter end of the spring is shown as connected to a cord 62 wound on aspool 63 on a long shaft 64 journaled lengthwise of the casing andprojecting through the forward end thereof to carry the adjusting knob3|', which is set in accordance with the air speed shown on indicator32', the spring tension being varied inversely with air speed. It willbe understood, of course, that the air speed may be set in automaticallyinstead of manually, if desired.

A still further modification is shown in Fig; '1. In this figure, theadjustable ring 2|" is vdisplaced in accordance with centrifugal forceby being connected to a fork 65 on the bottom of the gyroscope 22"through a long lever 6B which is pivoted between fork 61 on anadjustable nut 68, so that the pivot point may be adjustedlongitudinally by rotating a threaded rod B9 from'the air speed knob3|'. lBy this means, the ratio of movement of the gyro and the ring maybe varied in accordance with air speed, somewhat similarly to the formshown in Fig. 1,'the centralizing spring 25 in this instance being fixedto the casll'lg.

In this case, also, I so construct the indicator 42 at the forward partof the instrument that it shows rate of turn instead of centrifugalforce, so that the instrument may be used both as a rate of turnindicator and artificial horizon. For this purpose, the indicator 42 isdirectly connected to the top of the casing 22 by a long lever 60. Itwill be understood that the indicator 42' may be merely an index movableon a scale on the bezel or it may be a short scale, as in Fig. 4,readable upon an index on the bezel.l In this case, also, the ring 2|"is preferably truncated so as not to interfere with the index 42.

Still another method of introducing the air speed factor is by varyingthe speed of rotation of the rate gyro rotor in accordance with airspeed instead of by varying the linkage connection or spring stiffness.This may readily be done without any further apparatus than shown in anyone of the preceding figures by connect'- ing the suction outlet 8 ineach case to a Venturi tube in the air stream, which is designed to givea suction proportional to air speed. `When'this is done, it is obviousthat the adjustment for air speed otherwise made by knob 3| or knob 3|',as the case may be left untouched for moderate variations in air speedwhich would result in comparable changes in rotor speed, but fo'r largerspeed changes, some adjustment of knob 3| or' 3 would probably benecessary since rotorspeed does not continue to vary as a directfunction o f the pressure at the nozzle as the rotor speed becomesgreat.

I am aware that this method involves also a change in the rotor speedof, and' velocity'of air exhaust from, the horizon gyro, but this isvnot a serious disadvantage since the erection rate will not bematerially affected, as both the rotor speed and force of the air jetswill'vary'at about the same proportion, and therefore the rate oferection will remain substantially unchanged.

While I have apparently described a number of forms of the invention,the forms are closely related. Thus, the form of the invention shown inFig. 6, in which the tension of the centralizing spring is variedinversely with air speed, and the form of the invention described inWhich the air speed factor is introduced through varying the rotorspeed, are both species of the same broad principle of introducing theair speed factor by varying with air speed the extent of precession thatoccurs during a turn at any given rate, since the extent of precessionvaries inversely with the spring tension and directly With the rotorspeed. Also, the idea of showing rate of turn indications on the face ofthe instrument, although only shown in Fig. 7, is readily applicable tothe forms shown in Figs. 1 to 5, as will be readily apparent.

As many changes could be made in the above construction and manyapparently widely different embodiments of this invention could be madewithout departing from the scope thereof, it is intended that all mattercontained in the above description or shown in the accompanying drawingsshall be interpreted as illustrative and not in a limiting sense.

Having described my invention, what I claim and desire to secure byLetters Patent is:

l. An attitude indicating instrument for aircraft including a gyroscopicartificial horizon having a normally horizontal -index member controlledthereby, a rate of turn gyroscope, a reference member for the horizonindex member comprising a movable ring having diametrically oppositenormally horizontal reference positions thereon, and means for movingsaid ring under control of the rate of turn gyroscope.

2. An attitude indicating instrument for aircraft including a gyroscopicartificial horizon having a normally horizontal index member controlledthereby, a reference member for the horizon index member comprising amovable ring having diametrically opposite normally horizontal referencepositions thereon, a device responsive to turn of the aircraft about itsvertical axis, and means operatively connecting said ring and saiddevice.

3. In a gyroscopic articial horizon for dirigible craft, agyro-vertical, an index stabilized therefrom, a stationary referencemember readable With said index indicating the real attitude of thecraft about its roll axis, a movable reference member readable with saidindex indicating the virtual attitude of the craft about its roll axisduring turns, a device responsive to rate of turn of the craft about itsvertical axis for controlling said movable reference member, and meansfor adjusting said device in accordance with the air speed of the craft.

4. An attitude, proper bank angle and rate of turn indicating instrumentfor aircraft comprising an artificial horizon having an index controlledthereby, rotatable about a horizontal foreand-aft axis, a fixed indexmember, a member having separate reference indications thereon, saidmember being rotatable about said axis, one of said indications beingreadable with the index member controlled by the artificial horizon toprovide an indication of the virtual attitude of the aircraft about itsroll axis during turns, and the other of said reference indicationsbeing readable with the xed index member to provide an indication of therate of turn of the craft about its vertical axis, and a deviceresponsive to the rate of turn of the craft about its vertical axisoperatively connected to rotate said rotatable member.

5. An instrument as claimed in claim 4, in-

cluding a stationary reference member for the index controlled by thearticial horizon, the same providing an indication of the real attitudeof the aircraft about its roll axis.

6. An instrument for indicating the real and virtual attitude of a craftabout its roll axis during turns comprising a gyroscopicartificial-horizon having a casing with a fixed reference member thereonand a horizon index rotatable relative to the reference member about afore-andaft axis and readable therewith to indicate the real attitude ofthe craft, a second reference member mounted on said casing to turnrelative to said horizon index about said axis and readable therewith toindicate the virtual attitude of the craft, a device responsive to therate of turn of the craft in azimuth connected to said second referencemember to turn it about lsaid axis.

FREDERICK D. BRADDON.

